A circuit board used to mount various types of electronic components, such as a semiconductor element, a heater element, and a Peltier element, includes a ceramic sintered body and a metal wiring layer provided on at least one primary surface thereof, and an electronic apparatus including this circuit board and at least one electronic component mounted on the metal wiring layer thereof with an electrode pad or the like interposed therebetween has been used for various types of instruments.
In addition, the circuit board as described above is required so that the metal wiring layer is not likely to be peeled away from the ceramic sintered body due to heat generated during operation of the electronic component to be mounted. Hence, in order to improve the adhesion strength between the ceramic sintered body and the metal wiring layer, a glass is contained in a paste which forms the metal wiring layer provided on at least one primary surface of the ceramic sintered body, and the metal wiring layer is provided thereon with a glass layer interposed therebetween.
For example, PTL 1 has proposed a copper conductive paste formed from at least a conductive powder containing a copper powder as a primary component, a glass frit, and an organic vehicle. In this copper conductive paste, the glass frit contains at least a borosilicate zinc glass frit which has a softening point is 700° C. or less and a contact angle of 60° or less to a film formed from a copper powder, the surface of which is not substantially oxidized, in a nitrogen atmosphere at 900° C.; and a borosilicate glass frit which has a softening point of 700° C. or less and a solubility of 1 mg/cm2·hr or less to an aqueous sulfuric acid solution having a concentration of 10 percent by mass at 25° C.